Historic transducers: Balanced armature receiver (BAR)

Abstract

The oldest telephone receiver is the Balanced Armature Receiver (BAR) type, and it is still in use. The original technology goes back to the invention of telephone receiver by A. G. Bell in 1876. Attraction and release of the armature are controlled by the current from the coils, which generates electromagnetic fields [Hunt (1954) Chapter 7, and Beranek and Mellow (2014)]. As the electrical current goes into the electric terminal of the receiver, it generates an AC magnetic field which direction is perpendicular to the current. Due to the polarity between the permanent (DC) magnet field and the generated AC magnetic field, an armature (which sits within the core of the coil and the magnet) feels a force. The very basic principles for explaining this movement in a gyrator, a fifth circuit element introduced by Tellegen in 1948, along with an inductor, a capacitor, a resistor, and a transformer. This component represents the anti-reciprocal characteristic of the system. This study is starting from comparing the BAR type receiver to the moving-coil loud speaker. We believe that this work will provide a fundamental and clear insight into this type of BAR system.